On Mon, Aug 20, 2007 at 11:14:08PM +0200, Peter Zijlstra wrote: > On Mon, 2007-08-20 at 13:27 -0700, Christoph Lameter wrote: > > On Mon, 20 Aug 2007, Peter Zijlstra wrote: > > > > > > Plus the same issue can happen today. Writes are usually not completed > > > > during reclaim. If the writes are sufficiently deferred then you have > > > > the > > > > same issue now. > > > > > > Once we have initiated (disk) writeout we do not need more memory to > > > complete it, all we need to do is wait for the completion interrupt. > > > > We cannot reclaim the page as long as the I/O is not complete. If you > > have too many anonymous pages and the rest of memory is dirty then you can > > get into OOM scenarios even without this patch. > > As long as the reserve is large enough to completely initialize writeout > of a single page we can make progress. Once writeout is initialized the > completion interrupt is guaranteed to happen (assuming working > hardware).
Although interestingly, we are not guaranteed to have enough memory to completely initialise writeout of a single page. The buffer layer doesn't require disk blocks to be allocated at page dirty-time. Allocating disk blocks can require complex filesystem operations and readin of buffer cache pages. The buffer_head structures themselves may not even be present and must be allocated :P In _practice_, this isn't such a problem because we have dirty limits, and we're almost guaranteed to have some clean pages to be reclaimed. In this same way, networked filesystems are not a problem in practice. However network swap, because there is no dirty limits on swap, can actually see the deadlock problems. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/